Telegraph transmitter



Aug. 29, 1939 c. w. WINTER. JR EJW BM TELEGRAPH TRANSMITTER Filed April 8, 1957 If J1 me warm:

.surnrranmmmrrm INVENTOR Ckarle's IV Mul er, 1;:

BY A496 A Qua /[M6 kLATTORNEYS ATES PATENT OFFICE TELEGRAPH TRANSMITTER Jersey City, N. J., a corporation of Delaware Application April 8, 1937, Serial No. 135,609

6 Glaims.

My invention relates to radio telegraph transmitters and more particularly to an improved circuit for operating transmitters aboard aircraft in such a manner that the frequency of the transli mitted signals does not vary during relatively short time intervals.

in various tests which I have made, I have. found that when radio telegraph transmitters of the master oscillator-power amplifier type are p- 10 erated aboard aircraft with conventional type voltage supply circuits, an appreciable chirp is present in the emitted signals. The word chirp", as used herein, indicates the action or character of signals whose transmitted frequency varies during a relatively short time interval, for example, the time interval required for transmit-.

ting a dot or a dash.

Signals that chirpf are diflicult to copy due to the fact that the beat note in the receiving head m set starts at one frequency when the signal, e. g., a dot or dash, begins and is at an audibly different frequency at the end of the signal.

An object of my invention is to provide a radio telegraphic transmitter for aircraft that will w transmit signals whose frequency will not vary during relatively short time intervals.

Another object of my invention is to provide filament compensating means in the voltage supply circuit of a master oscillator-power amplifier 3c transmitter to prevent "chirping" of the transmitted signals.

In accordance with the present invention, I'

'The novel features of my invention are setforth with particularity in the appended claims.

no The invention itself, however, both as to organization and method of operation may be easily understood lrom the following description taken in conjunction with the accompanying drawing,

which illustrates one non-limiting embodiment of so my invention.

Referring now to the drawing, which is primarily a wiring diagram of the transmitter of my invention, the transmitter comprises vacuum tubes it and it having filaments E2. The vacuumtube to ill is the master-oscillator and the vacuum tubel l (m. lids-66) is the power-amplifier. tlonnected in series with the filaments It is a variable resistor it and con nected electrically in shunt with this resistor is a make and break switch it controlled by keying relay 85 which is in turn controlled by a tele- 5 graph key it. v

For the sake'oi simplicity, the grid and plate electrodes of the vacuum tubes it and l i have been omitted, the filaments being the only tube electrodes shown since they are of primary imlil portance in the present invention. The tubes ill and l i may he of conventional type and may have any desired number of grid and plate electrodes.

The voltage that is applied during operation of the transmitter to the plate electrodes of the tubes lli it and ii is obtained from a dynamotor illustrated diagrammatically at W. This dynamotor has a motor end it and a generator end it. The plate voltage is supplied from this generator to to the plates of the tubes it and ii in a well no known manner.

The voltage for operating the motor it and for energizing the filaments ll of the vacuum tubes it and l l is supplied by a storage battery shown diagrammatically at it. The flow of current from this battery it is controlled by the starting switch M. The fixed resistor 22 is supplied for reducing the voltage from the storage hattery all, whenever necessary, to the exact amount required for properly operating the filaments ill of the so vacuum tubes and H.

The operation of this transmitter and the means employed for overcoming its normal chirping" tendencies will he understood from the following description. so

The first step required to start the operation of the transmitter is to close the starting switch 2i. This efl'ects a flow of current from the storage battery in that starts the dynamotor l l and at the same time supplies voltage to the filaments l2 oi no the vacuum tubes it and Ills. The current sup plied to the filaments I? from the battery 20 flows through .the .fixed resistor it and through the variable resistor ill. At this point the telegraph rent supplied to the filaments is compelled to flow 5c through thevariable resistor it. 7

At this stage of the operation the grids of the vacuum tubes in and ll are biased to cut-oi! according to a conventional method, and therefore no plate current is being drawn by the trans- 56 will not vary during mitter. Consequently, the input current to the dynamotor is relatively small.

If the telegraph key l6 isnow depressed, the grid bias of the tubes I 0 and II is changed to normal, resulting in a flow of normal operating plate current through these tubes. Simultaneously, the plate current load of the transmitter is thrown on the generator end IQ of the dynamotor l1 and this in turn causes a sudden rise in the input current to the motor end III of the dynamotor. This increase in current drain from the storage battery 20 causes the voltage at the terminals of. the battery to drop and also causes additional RI drop in the lines between the battery and the dynamotor l'l. Since the transmitter is located near the dynamotor this voltage drop, is also experienced at the filaments of the transmitter vacuum tubes l0 and II.

The several operations described just above resulting from pressing the telegraph key occur the instant the key is closed. During a relatively short time interval, such as for example, that required to transmit a dash signal, i. e., 60 milliseconds, there are two operations that take place more or less linearly with respect to time and which normally cause the emitted signal to chirp. They are as follows:

1. The dynamotor armature slows down due to added secondary load and reduced voltage at its input terminals.

2. The temperature of the vacuum tube filaments decreases due to the reduced voltage at their terminals.

In view of the fact that the frequency of the master oscillator III is efiected both by filament temperature and plate voltage, it will be seen from the above description that the emitted frequency will be different at the beginning and end of a transmitted signal such as, for example, a dash. In actual practice the reduction of filament and plate voltage both effect an increase in the frequency of the signal transmitted.

One of the principal features of my invention as applied to the specific embodiment shown in the drawing consists of connecting, in the manner shown, avariable resistor l3 in the filament circuit of the vacuum tubes l0 and l I. This variable resistor serves as a compensating resistor as will appear from the following description. The make and break switch II, which may consist of a separate set of contacts on the keying relay l5, short circuits this compensating resistor [3 each time the telegraph key I6 is pressed. Now, if this compensating resistor I 3 is adjusted to give the same filament voltage when the telegraph key I6 is up and when it is depressed, the voltage applied to the filaments l2 of the vacuum tubes l0 and H the operation of the tube. Consequently, the temperature of the filaments l2 will remain constant. The chirp or frequency varying characteristic normally caused by varying filament voltage will accordingly be eliminated by means of this compensating resistor l3.

As mentioned above, however, some of the "chirp in the transmitted signal is caused by the varying voltage supplied to the dynamotor, resulting in the latter slowing down under load conditions] Therefore, to eliminate the chirp in the transmitted signal caused by variations in the dynamotor operation, the value of the compensating resistor i3 is increased so that the filament voltage actually rises a small amount when the telegraph key 56 is depressed. I have found that by so regulating the value of this resistor L3.

it compensates for the slowing down of the dynamotor armature. The reason for this is that when the voltage is raised the time rate of the filament temperature rise is approximately equal to the time rate of the armature speed decrease and, since these two effects are working in opposite directions on the master-oscillator frequency, the result is a signal of substantially constant frequency which is audibly free of chirp.

By means of the compensating filament resistor arrangement of my invention described above, especially in connection with a masteroscillator power-amplifier type of radio telegraph transmitter, the signal emitted from the transmitter will be audibly free of chirp or frequency variation. Also, the vacuum tube filament voltage is maintained at a constant value, which not only serves to eliminate chirp but also eifectively increases the life of the vacuum tube filaments.

Various modifications of the system described above will occur to those skilled in the art and are intended to come within the scope of my invention. For example, the compensating resistor l3 may be connected in the filament circuit of the master-oscillator tube alone so that the control would be effected independent of the power amplifier. Any desired number of vacuum tubes of the oscillator and power amplifier type may be used. These tubes may employ a single grid or multiple grids. Also, the compensating filament resistor might be connected to the heater elements of cathode type vacuum tubes, although the control which compensates for the decrease of dynamotor speed could not be eifected a's efiic'iently as with the filament type of tube.

Instead of a dynamotor any other type of rotary power supply may be used, such as for example, a motor-generator. Thus, the primary source of power instead of being a storage battery might be an alternating current supply. When alternating current is used a motor-generator could be employed having an A. 0. motor mechanically connected to a D. C. generator. In such a case the filaments of the vacuum tubes could be heated through the intermediary of a suitable step-down transformer or from a suitable low voltage winding on the D. C. generator. The D. C. generator would also supply high voltage for the plates of the vacuum tubes.

The appended claims are addressed to some of the novel features of my invention.

I claim:

1. A radio transmitter comprising a vacuum tube having a filament, a rotatory power supply,

a source of power connected to said rotatory power supply for energizing the same, connection between said source of power and the filament of said vacuum tube for heating the same, a resistor connected between said source of power and said filament for compensating for the variations in power supplied to said filament and to said rotatory power supply during operation of said transmitter, and means for short circuiting and electrically disconnecting said variable resistor during certain stages in the operation of the transmitter, whereby the frequency of relatively short signals emitted from said transmitter remains constant.

2. A radio transmitter comprising a vacuum tube having a filament, a rotatory power supply, a source of power connected to said rotatory power supply for energizing the same, connection between said source of power and the filament of said vacuum tube for heating the same, a variable menace resistor connected between said source of power and said filament for compensating for the power variations in said transmitter during operation thereof, and means for short circuiting and electrically disconnecting said variable resistor during certain stages in the operation of the transmitter whereby the frequency of relatively short signals emitted from said transmitter remains constant.

3. A radio telegraphic transmitter comprising a vacuum tube having a filament, a motor generator, a source of power connected tosaid motor generator for energizing the same, connection between said source of power and the filament of said vacuum tube for heating the same, a variable resistor connected between said source of power and said filament for compensating for the supply voltage variations to said transmitter during operation thereof, and a keying relay for short circuiting and electrically disconnecting said variable resistor during certain stages in the operation of said transmitter,'.whereby the frequency of relatively short signals emitted from said transmitter remains constant.

4. A radio telegraphic transmitter comprising a vacuum tube having a filament, a dynamotor, a source of power connected to said dynamotor for energizing the same, connection between said source of power and the filament of said vacuum tube for heating the same, a variable resistor connected between said source of power and said filament for compensating for the supply voltage variations to said transmitter during operation &

thereof, a keying relay for short circuiting said variable resistor during certain stages in the operation of said transmitter, and a telegraph key for alternately energizing and tie-energizing said keying relay by which said variable resistor is alternately electrically connected and disconnected in circuit between said power supply and said filament whereby the frequency of relatively short signals emitted from said transmitter remains constant.

5. A method for maintaining substantially constant the frequency output of a telegraphic vacuum tube transmitter during time intervals of dots and dashes, comprising decreasing the electrical resistance in-the filament circuit of the transmitter to compensate for the voltage drop in the filament supply circuit caused by increased current drain in that circuit during the trans: mission of dots and dashes.

6. A radio telegraphic transmitter comprising a vacuum tube, a source of power' for furnishing filament voltage to said tube, a resistor connected in circuit between said source of power and the filament of said tube, and a second source of power for furnishing plate voltage to said tube, and means responsive to operation of the transmitter for short circuiting said resistor to reduce the resistance in said circuit to compensate for drop in the filament and plate voltages applied to the tube during transmission of dots and dashes.

CHARLES W. WINTER, J2.

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